Method and device for notching tubes and the tube thus obtained

ABSTRACT

The invention relates to a method of notching a tube. The inventive method is characterised in that it comprises the to-and-fro movement of at least one pressure roller. During said movement, the aforementioned roller applies pressure locally to the wall of the tube ( 1 ) and plastically deforms same. The movement of the pressure roller is produced by a combination of at least two other movements, namely: a first essentially rectilinear to-and-fro movement, during which the roller rolls against the wall of the tube ( 1 ); and a second forward movement, the resultant of which is essentially perpendicular to the direction of the first movement. In this way, the tube ( 1 ) is plastically deformed in at least two movements of the pressure roller.

The invention relates to a process and a device for the notching oftubes.

The word “tube” here indicates a hollow body, specifically cylindrical,which may be open or closed, and which is made of metallic material orany other similar material.

In many industrial areas, notches must be made in hollow tubes. Thistype of notching is done, for example, in support bars with a ratchetfor a hand brake, pinion racks, or in structures for headrests inautomotive vehicles.

In this last specific use, the notches in the tubes must have sharp,clean edges in order to get accurate adjustment of the height of theheadrest, and in order to prevent the headrest from being easily shiftedand disturbed when a slight pressure is applied, for example by a child.

Structures for headrests with the tube in the shape of a notched U aredescribed, for example, in the following documents:

-   -   Requests for patent in France, published under numbers        2,755,915, 2,751,926, 2,734,612, 2,734,216, 2,721,267,        2,704,188, 2,666,771;    -   Requests for European patents, published under numbers        1,108,607, 1,046,541, 953,477, 875,417, 743,222, 687,590,        412,307;    -   American patents published under U.S. Pat. Nos. 5,478,136,        5,398,996, 5,257,853, 5,165,754, 4,390,209.

We already know, from prior practice, about various processes whichallow a series of sharp-angle notches to be made in tubes, whether ornot the material is removed.

Notching the tubes by machining, where the material is removed, presentsnumerous drawbacks and is no longer considered, because it makes thetube much too fragile.

In return, many processes for notching a tube that do not involveremoving the material are proposed in prior practice.

Document EP-A-0 974 409 describes a notching process that implements anepicycloid train riveting machine, with a spherical cap, which isalready known, and which, instead of its rivet-punch, consists of apunch that is adapted to the profile of the notching to be executed.This punch is engaged in a complex movement that breaks down into atranslation movement and an orbital movement. The tube to be notched isplaced in a groove in a fixed half-shell, a moveable half-shell or ablank-holder that has a groove located opposite the groove in the fixedhalf-shell.

The procedure described in document EP-A-0 974-409 has numerousdrawbacks. In particular, the productivity achieved is very low, and notvery compatible with the requirements of the automobile manufacturingsector. Moreover, as mentioned in this earlier document, the movement ofthe punch is complex and can prove difficult to control, so that thequality of the notches produced on the tube is subject to variations,and this in spite of a blockage in the rotation of the notching punch byan anti-diverter.

Document FR-A-2 805 481 describes a tube notching process that is doneby press stamping. The process uses a matrix that consists of parts; alower matrix, a right upper matrix and a left upper matrix. A groove isarranged in the lower part of the matrix to accept the tube to benotched. Then the parts of the left and right upper matrix are platedagainst the tube to be notched, and the matrix obtained featuresthrough-holes, through which the punches stamp the tube.

The process described in document FR-A-2 805 481 has numerous drawbacks.In particular, in order to minimize the amplitude of weakening by shearforces, it is necessary to adjust the dimensions of the indented partand the notch. If this is not done, the notches may have burrs: notchingtubes by press deformation as described in document FR-A-2 805 481,involves sagging, which requires additional machining in order to obtainsharp angles. Productivity obtained by the stamping process is low.

In order to control the thickness and section of tubing during stampnotching, document EP-A-1 112 791 offers placement of a mandrel andpressing in multiple passes. This type of process does not allowassurance of high productivity and cannot, by its very nature, beimplemented with closed tubes.

Document WO-A-01/15827 describes a notching device that comprises asliding forming tool.

Other tube notching processes are described in documents DE-U-29717174,De-U-29714315, EP-A-0 867 334.

The invention is intended to provide a process and a tube notchingdevice that does not have the drawbacks that the processes and devicespresent up to now.

The invention is intended, specifically, to provide a process whichassures an increased productivity, a greater regularity in shape for thenotches, absence of burrs and repeated machining, because the notchesare formed without removing the material and without significantweakening in the tube's resistance.

To this end, the invention relates, first of all, to a notching processfor a tube, where this process consists of a back-and-forth motion of aleast one pressing roller; during this movement the roller presseslocally and plastically deforms the wall of the tube, where the movementof the pressing roller is formed by the combination of at least twomotions, namely:

-   -   a first motion, largely rectilinear, back-and-forth, during        which the roller rolls against the wall of the tube;    -   a second motion, known as “forward”, whose result is largely        perpendicular to the direction of the first motion, where the        plastic deformation is also obtained in at least two passes of        the pressing roller.

According to one characteristic, the process consists of an inspectionstep of one parameter selected from among the group consisting of:pressing force of the pressing roller on the tube, the position of theroller while it is in contact with the tube.

Secondly, the invention relates to a machine for the implementation of aprocess defined above, where this machine comprises a means fortemporarily holding a tube in a predetermined position and a means ofmotorized driving of the pressing rollers following their first motion.

According to various methods of embodiment, the machine features thefollowing characteristics, which may or may not be combined:

-   -   it comprises a means for causing the second motion, called the        forward motion, of the pressing roller, in a controlled manner,        where these means consists of a means chosen from among the        group comprising springs, activators such as jacks;    -   it consists of a motorized roller carrier trolley, where this        trolley is driven back and forth following the first motion, and        where it is mounted mobile in rotation around an axis that is        largely perpendicular to the direction of this first motion;    -   it consists of three pressing rollers whose diameters are        largely identical and whose rotational axes are largely aligned        following the direction of said first back-and-forth motion;    -   it consists of a means of servo-system for moving the pressing        rollers as a function of at least one parameter chosen from        among the group consisting of: the support force of the pressing        roller on the tube, the position of the roller during its        contact with the tube;    -   the servo-system is of the electro-hydraulic type.

Thirdly, the invention relates to a headrest tube obtained byimplementing a process ad defined above.

Other subjects and advantages of the invention will become apparentduring the following description of means of production and descriptionwhich will be performed by referring to the attached drawings, in which:

FIG. 1 is a top view of a notching machine that implements the processin the invention, according to one method of embodiment;

FIG. 2 is a lateral view of the machine in FIG. 1, according to arrowII;

FIG. 3 is a lateral view of the machine in FIG. 1, according to arrowIII.

The following description will be carried out in relation to thenotching of a U-shaped tube of the type used in conventional headrestframes. As the skilled craftsman will understand, the process and thedevice in the invention also allow notches to be produced in other typesof tubes, such as, for example, those used for pinion racks or supportbars with ratchet for hand brake.

In the figures, a U-shaped tube 1 is held in position by a means 2 suchas a groove matrix, in the work volume of a machine 3.

In the manner of embodiment shown, tube 1 is introduced into volume V,by a movement according to arrow F, where the two largely parallelbranches 4 and 5 of tube 1 extend following direction D1.

This direction D1 shall be considered to be vertical, in the remainderof this description. It shall nevertheless be understood that thisarrangement is being used only arbitrarily, for purposes of simplicity.In effect, as the craftsman will understand, functioning of the machineis in no way influenced by the assignment of direction D1.

Maintaining the position of the tube in its receptacle grooves may beachieved using means such as tightening clamps, for example.

In the manner of embodiment show, the tube is of a largely circularsection. It shall nevertheless be understood that the process accordingto the invention may be implemented for tubes of oval or polygonalsection.

Machine 3 is equipped with three profiled rollers 6, 7, and 8, mountedin rotation following direction D1.

In one manner of embodiment, these three rollers 6, 7, and 8 are mountedon a sliding trolley following direction D2, where this trolley isitself mounted jointed according to direction D1 relative to the machine3's frame, where this frame is held on tube 1 to be notched. A means forcontrolled pressurizing ensures the support of rollers 6, 7 and 8 ontube 1 to be notched.

In a first specific implementation, these means comprise a torsionspring mounted on axle 10.

In a second specific implementation, these means consist of acompression spring mounted between a support bearing 11 and slidingchassis 12 which supports rollers 6, 7 and 8, this spring is drawn byreference 13 in FIG. 1. This compression spring 13 is, as a variation,combined with the torsion spring mounted on axle 10 on trolley 12. As avariation, a single-effect actuator is installed instead of spring 13.

The first and second methods of embodiment indicated above produce amotion of the roller-mount trolley that is largely rectilinear,following direction D2.

The applicant has nevertheless stated that such a largely rectilinearmovement could lead to significant residual constraints on the nicks,i.e. slight flaws in shape in these nicks following significant plasticdeformation of the material comprising tube 1.

Also, in a third embodiment, roller mount trolley 12 is controlled, inits rotational movement about axis of rotation 10, by a means such as adouble-effect actuator.

The control of the movements of the actuator shaft is enacted, in onevariation, as a function of trolley motion. In another variation,controlling the movement of the actuator shaft is enacted as a functionof the strain borne by the trolley as the roller passes over tube 1,where this strain reflects the force of plastic deformation borne by thetube material 1 during notching.

Thus it is possible to use variable pressure to work rollers on tube 1,for example increasing, then largely constant, then decreasing. Thecraftsman will know, for a specific tube material, how to experimentallyadapt the pressure profile that offers the compromise that is mostadapted to his fabrication time and residual constrain requirements.

The forward and backwards movements of the trolley that carries rollers6, 7 and 8 are motorized, and rapid, on an order of several tens toseveral hundreds of back-and-forth motions per minute.

The applicant has stated that the process as it was just describedallows extremely significant gains in productivity, relative topreviously known processes, all the while ensuring a great regularity inthe shape of the notches, where the material the tube is made of has notthinned out at the end of the notch.

Machine 3 can consist of one, two or more than two notches. The notchesmay be profiled for the production of one or more notches in the tube.

The notches may be arranged with their axes of rotation largelyparallel, as shown.

In other manners of embodiment, not shown, axes of roller rotation arenot aligned, for example for the formation of negative notches. Theposition of axes of rotation of the rollers is, in one manner ofembodiment, subject to the position or the force of the roller on thetube being notched.

In this case, the rollers can be arranged according to several rows thatare largely parallel, so that the make two or more than two notches atthe same time.

As the craftsman will easily understand, by clamping tube 1 according toan angle determined relative to direction D3 in FIG. 1, it is possibleto arrange the notches in any orientation: interior surface of the tubeas shown in FIG. 1 of document FR-A-2 805 481, or external surface ofthe tube as shown in document Fr-A-2 771 686, or yet again towards theback of the headrest as shown in document Fr-A-2 764 850, or towards thefront of the headrest as described in document Fr-A-2 758 296.

The process according to the invention allows notching of headrest frametubes to be done in a very short time, on an order of a few seconds.

1. Process for notching a tube, comprising a back and forth motion of at least one pressing roller, movement during which this roller locally presses and plastically deforms the tube wall, and where the movement of the pressing roller consists of a combination of at least two displacements, namely: a first motion, largely rectilinear, back and forth, during which the roller rolls against the tube wall; a second motion, called a forward motion, whose result is largely perpendicular to the direction of the first motion, the plastic deformation of the tube thus being obtained in at least two passes of the pressing roller.
 2. Notching process according to claim 1, further comprising an inspection stage where a selected parameter is chosen from the group consisting of: the force of the pressing roller on the tube, the position of the roller during its contact with the tube.
 3. Machine for the implementation of the process according to claim 1 comprising a means of temporarily holding at least one tube in a predetermined position, and a means of motorized drive of the pressure rollers following their first motion.
 4. Machine according to claim 3, comprising a means to cause the second motion, known as the forward motion, of the pressing roller, in a controlled manner, these means comprising a means chosen from the group consisting of springs, activators such as jacks.
 5. Machine according to claim 3, comprising a motorized roller-mount trolley, the trolley being driven back and forth following said first motion and being mounted mobile in rotation around an axle that is largely perpendicular to the direction of this first motion.
 6. Machine according to claim 3, comprising three pressure rollers of diameters that are largely identical, and whose rotational axes are largely aligned according to the direction of the first back and forth motion.
 7. Machine according to claims 3, comprising a means of servo-system for the pressure roller displacement, as a function of at least one parameter selected from among the group consisting of: the force of the pressure roller on the tube, the position of the roller upon contact with the tube.
 8. Machine according to claim 7, wherein the servo-system is of the electro-hydraulic type.
 9. Tube obtained by the implementation of the process according to claim 1, wherein the tube for a headrest support. 